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C Lee

Publications and source records attributed to C Lee.

At least 541 records · Page 30Linked to original sources
PubMed1995

A general model of invariant chain association with class II major histocompatibility complex proteins.

The binding of invariant chain to major histocompatibility complex (MHC) proteins is an important step in processing of MHC class II proteins and in antigen presentation. The question of how invariant chain can bind to all MHC class II proteins is central to understanding these processes. We have employed molecular modeling to predict the structure of class II-associated invariant chain peptide (CLIP)-MHC protein complexes and to ask whether the predicted mode of association could be general across all MHC class II proteins. CLIP fits identically into the MHC class II alleles HLA-DR3, I-Ak, I-Au, and I-Ad, with a consistent pattern of hydrogen bonds, contacts, and hydrophobic burial and without bad contacts. Our model predicts the burial of CLIP residues Met-91 and Met-99 in the deep P1 and P9 anchor pockets and other detailed interactions, which we have compared with available data. The predicted pattern of I-A allele-specific effects on CLIP binding is very similar to that observed experimentally by alanine-scanning mutations of CLIP. Together, these results indicate that CLIP may bind in a single, general way across products of MHC class II alleles.

Alleles↗
PubMed1995

Postnatal maturation of the blood-brain barrier for unbound bilirubin in newborn piglets.

The postnatal maturation of the blood-brain barrier (BBB) for unbound bilirubin was studied in 2-day- and 2-week-old piglets. Hyperbilirubinemia was induced by bolus infusion of bilirubin at 25 mg/kg followed by continuous infusion of 20 mg/kg/h for 3 h. During the study period, arterial blood pH and blood gas tensions, serum osmolarity, and mean arterial blood pressures were within the physiologic range. Brain bilirubin content and the brain/blood distribution ratio for bilirubin were higher in the 2-day-old than in the 2-week-old piglets. In both age groups, regional brain bilirubin concentration and brain/blood ratios were higher in subcortical regions (cerebellum and brainstem) than in the cerebral cortex. We conclude that in newborn piglets the blood-brain barrier for unbound bilirubin matures with increasing postnatal age and that irrespective of maturity the relative permeability of the BBB for bilirubin appears higher in subcortical than in cortical regions.

Aging↗
PubMed1995

Arachidonic acid metabolism by human cytochrome P450s 2C8, 2C9, 2E1, and 1A2: regioselective oxygenation and evidence for a role for CYP2C enzymes in arachidonic acid epoxygenation in human liver microsomes.

The membrane-bound endogenous fatty acid arachidonic acid can be released from membranes by phospholipases and then metabolized to biologically active compounds by cyclooxygenases, lipoxygenases, and cytochrome P450 (CYP) enzymes. In the liver the CYP pathway is the most significant. Liver CYP arachidonate products include epoxyeicosatrienoic acids (EETs) and monohydroxylated products (HETEs). We examined metabolism of [1-14C]arachidonic acid by a panel of 10 human CYP enzymes expressed in HepG2 cells. In the absence of expressed CYP enzymes, control HepG2 cell microsomes generated only small amounts of omega- and omega--1-OH arachidonic acid (ratio 2:1). Microsomes from HepG2 cells expressing CYP2C8, 2C9, 1A2, and 2E1 were 7-21 times more active than microsomes from the HepG2 controls. CYP2C8, 2C9, and 1A2 principally generated epoxygenase products; 36 to 48% were in the form of EET-diols, reflecting host HepG2 microsomal epoxide hydrolase activity. CYP2C8 and 2C9 formed more 14,15- and 11,12-EET than did CYP1A2, while CYP1A2 formed more 8,9-EET. CYP2C9 also generated a peak with the retention time of 12-HETE. CYP2E1 generated omega--1-OH arachidonic acid and, to a lesser extent, omega-OH arachidonic acid (ratio 2:1). A small amount of epoxygenase activity was also detected for CYP2B6; its overall activity, however, was only about twice control levels. Activities of CYP2A6, 3A3, 3A4, and 3A5 were low and limited to the omega-/omega--1-OH arachidonic acid peak; CYP2D6 was inactive. Microsomes prepared from three individual human livers varied threefold in total arachidonic acid metabolism. For all three livers omega-OH arachidonic acid was the major product (up to 74% of total metabolites). Epoxygenase products constituted 14 to 28% of the total products; 60 to 83% of those were EET-diols, indicating that the human liver microsomes have substantial EET-epoxide hydrolase activity. 11,12-EET was the major EET for two livers and 14,15-EET for the third. The CYP2C inhibitor sulfaphenazole depressed human liver microsomal epoxygenase activity by 50% at 50 microM, while alpha-naphthoflavone inhibited arachidonic acid epoxygenase activity by 27% at 2 microM and by 32% at 10 microM. Collectively, these findings suggest that human liver microsomal arachidonic acid metabolism is catalyzed principally by CYP2C enzymes. CYP1A2, CYP2E1, and possibly CYP2B6 are likely to play more minor roles, though their contribution may be enhanced by exposure to inducers of those enzymes. CYP2A6, CYP2D6, and CYP3A enzymes are unlikely to make any significant contribution.(ABSTRACT TRUNCATED AT 400 WORDS)

Arachidonic Acid↗
PubMed1995

Prevention of cell death induced by tumor necrosis factor alpha in LNCaP cells by overexpression of sulfated glycoprotein-2 (clusterin).

Sulfated glycoprotein-2 (SGP-2) expression has been associated with programmed cell death in the prostate, but its exact role remains unclear. The present study was carried out in an attempt to establish the function of SGP-2 in programmed cell death using tumor necrosis factor (TNF) alpha-induced cytotoxicity in LNCaP cells as the model system. LNCaP is an androgen-sensitive, human prostatic cancer cell line that responds to TNF in culture by undergoing programmed cell death, as determined by the loss of cell number, failure to exclude trypan blue, detection of DNA fragmentation, and increased release of previously incorporated [3H]thymidine. Immunocytochemical staining for SGP-2 was weak but evident in LNCaP cells. Following treatment with TNF alpha, there was a time-dependent increase in SGP-2 staining, the intensity of which peaked at 2 h and declined thereafter. SGP-2 staining in LNCaP cells was undetectable prior to the onset of DNA fragmentation at 6 h of TNF treatment. This observation indicated that TNF-induced cell death in LNCaP cells was characterized by an initial transient elevation of SGP-2, followed by a period of SGP-2 depletion that preceded cell death. Transfection of LNCaP with a 21-base oligonucleotide antisense to SGP-2 resulted in a significant increase in cell death that was sequence specific and was accompanied by a reduction in SGP-2 biosynthesis. These findings supported the concept that SGP-2 depletion, rather than its expression, was associated with cell death. Finally, stable transfection and subsequent overexpression of SGP-2 in LNCaP cells resulted in resistance to the cytotoxic effect of TNF. These results have provided evidence to indicate that SGP-2 plays a role in the protection of TNF-induced cell death in LNCaP cells.

Animals↗
PubMed1995

Photosensitization by 3,3'-dihexyloxacarbocyanine iodide: specific disruption of microtubules and inactivation of organelle motility.

Photodynamic therapy is a useful new direction for cancer treatment. However, relatively little is currently known about the cellular targets and processes underlying the efficacy of these therapies. In this study, we report evidence of specific photosensitization of a novel intracellular target, cytoskeletal microtubules, that has great importance for cancer treatment. Photosensitization destroys microtubules, halts intracellular organelle motility processes, and leads to rapid cell death. We have examined the cell biological effects of photosensitization with the carbocyanine dye 3,3'-dihexyloxacarbocyanine iodide, which concentrates in mitochondria and the endoplasmic reticulum. Exposure of stained CV-1 kidney epithelial cells to as little as 30-120 s standard fluorescence excitation light caused disruption of the interphase microtubule network and complete inhibition of motility of the endoplasmic reticulum and all phase-contrast visible organelles, as specific effects of dye photoexcitation. Photoexcitation of rhodamine 123 or Hoechst produced neither of these effects. Furthermore, 3,3'-dihexyloxacarbocyanine iodide-mediated photodamage was specific to microtubules; other elements of the cytoskeleton, including vimentin intermediate filaments and actin stress fibers, were unaffected. We have reproduced the photoinactivation of microtubules in vitro with purified microtubule proteins.

Animals↗
PubMed1995

Identification of a discrete region of the G protein gamma subunit conferring selectivity in beta gamma complex formation.

The identification of multiple G protein beta and gamma subunit subtypes suggests a potential diversity of beta gamma heterodimers, which may contribute to the specificity of signal transduction between receptors and effectors. The assembly of beta and gamma subtypes is selective. For example, gamma 1 can assemble with beta 1 but not with beta 2, whereas gamma 2 assembles with both beta isoforms. To identify the structural features of the beta and gamma subunits governing selectivity in heterodimer assembly, a series of nonisoprenylated chimeras of gamma 1 and gamma 2 was constructed, and their interaction with beta 1 and beta 2 was assessed by their ability to direct beta expression to the cytosol in cotransfected COS cells. All of the gamma 1/gamma 2 chimeras were capable of interacting with beta 1 as judged by the cotransfection assay. Chimeras containing gamma 2 sequence near the middle of the molecule between two conserved sequence motifs were capable of interacting as well with beta 2. Among 12 divergent residues in this region, it was found that replacement of three consecutive amino acids in gamma 1, Glu-Glu-Phe (residues 38-40), with the three corresponding amino acids of gamma 2, Ala-Asp-Leu (residues 35-37), conferred the ability to assemble with beta 2. The reciprocal chimera containing Glu-Glu-Phe in the context of gamma 2 failed to assemble with beta 2. The last residue of this triplet is occupied by a leucine in all known mammalian gamma subunits except gamma 1 and appears to be a key determinant of the ability of a gamma subunit to assemble with beta 2. This locus maps to a region of predicted alpha-helical structure in the gamma subunit, likely to represent a point of physical contact with the beta subunit.

Amino Acid Sequence↗
PubMed1995

Automated instrument tracking in robotically assisted laparoscopic surgery.

This paper describes a practical and reliable image analysis and tracking algorithm to achieve automated instrument localization and scope maneuvering in robotically assisted laparoscopic surgery. Laparoscopy is a minimally invasive surgical procedure that utilizes multiple small incisions on the patient's body through which the surgeon inserts tools and a videoscope in order to conduct an operation. The scope relays images of internal organs to a camera, and the images are displayed on a video screen. The surgeon performs the operation by viewing the scope images rather than performing the traditional "open" procedure, where a large incision is made on the patient's body for direct viewing. The current mode of laparoscopy employs an assistant to hold the scope and position it in response to the surgeon's verbal commands. However, this results in suboptimal visual feedback, because the scope is often aimed incorrectly and vibrates due to hand trembling. We have developed a robotic laparoscope positioner to replace the assistant. The surgeon commands the robotic positioner through a hand/foot controller interface. To further simplify the human-machine interface that controls the robotic scope positioner, we report here a novel scope-positioning scheme using automated image analysis and robotic visual servoing. The scheme enables the surgeon to control visual feedback and to perform surgery more efficiently without requiring additional use of the hands.

Algorithms↗
PubMed1995

Hepatitis C genotypes in haemophilic patients treated with alpha-interferon.

The effect of alpha-interferon on the hepatitis C genotypes was examined in 25 anti-HCV-positive haemophilic patients. The rate of multiple HCV genotypes in patients who are likely to have mixed infections was also studied. Pretreatment results showed that 3/25 (12%) patients had a change in genotypes, whereas posttreatment this rose to 10/25 (40%). Seven of 10 (70%) patients who showed a change in genotype had a clinical response to alpha-interferon. Six of 25 (24%) patients showed a complete clinical response to alpha-interferon, and the majority of these were either type 2 or 3. This study supports previous evidence that type 1 is less likely to respond to alpha-interferon, and that alpha-interferon may alter the concentrations of the various circulating genotypes present in multiply-infected patients. There are many difficulties in studying hepatitis C in haemophilic patients due to the sequence heterogeneity within each individual, and this study has shown that no ideal method exists as yet for looking at HCV genotypes in multiply-infected individuals.

Alanine Transaminase↗
PubMed1995

Fourier transform infrared spectroscopy of dysplastic, papillomavirus-positive cervicovaginal lavage specimens.

To assess the utility of a new, rapid, economical procedure that may prove valuable in cervical screening, Fourier transform infrared (ir) spectroscopy was performed on 25 cervicovaginal lavage specimens from women referred for colposcopy on the basis of a cytological abnormality detected on their Pap smear and whose lavage specimen was positive for human papillomavirus. Of the 18 classed as CIN I or less by histopathology, 11 showed band frequencies that deviated only slightly from spectra that characterize normal cervical cells and 3 of 5 "atypia" specimens had spectra identical to normal. Two of 3 classed as CIN II had spectra only slightly more abnormal to these 11. In the case of 2 graded as CIN I, several bands were similarly altered in the direction of the pattern seen for 4 CIN III specimens. A further CIN I sample gave a spectrum that was even further shifted toward the latter and the remaining CIN I sample had a pattern that matched the 4 CIN IIIs. The most obvious change in each of the CIN IIIs was an additional peak at 972 cm-1 and this has been suggested as a key indicator for malignancy. One of the 3 CIN IIs had this peak. Other characteristic spectral changes were seen as well in the CIN III samples. High-risk HPV18 was present in 3 of the CIN III samples, as well as in one specimen classed as atypia, but having an abnormal ir spectrum. Low-risk HPV 6 or 11 was seen along in samples with a normal or slightly abnormal ir spectrum, but never in those that showed an ir pattern that was abnormal. The current study has therefore shown complete concordance between ir spectral findings and histopathology result in the case of CIN III specimens, but less precise matching for other grades of CIN. The spectral differences revealed by ir spectroscopy are likely to characterize molecular abnormalities in cervical cells during progression to cancer and may therefore have potential in assisting with clinical decision making. More studies will, however, be required to establish the place of this technique in cervical screening.

Colposcopy↗
PubMed1995

Epidermal growth factor-related peptides and the epidermal growth factor receptor in normal and malignant prostate.

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) are two closely related peptides that interact with cell-surface epidermal growth factor receptors (EGFR) to induce receptor tyrosine phosphorylation and activation of intracellular signal-transduction pathways. EGF appears to be the predominant EGF-related growth factor in the normal prostate and in benign prostatic hyperplasia (BPH). Evidence indicates that EGF and TGF alpha are important for maintainence of the structural and functional integrity of the benign prostatic epithelium. The EGF-related peptides are primarily localized to the secretory epithelium of the benign prostate, and their production and secretion is augmented by the presence of circulating androgens. EGFR are located in the basal/neuroendocrine (NE) compartment of the benign prostate and exhibit relatively androgen-independent expression. The EGF-related peptides and EGFR are also present in neoplastic prostatic tissues. There is currently no direct evidence to implicate EGFR activation in the pathogenesis of BPH. However, the EGF-related peptides appear to play a functional role in the growth of prostatic carcinoma cells, with TGF alpha being the predominant growth factor. Numerous investigators have demonstrated the functional significance of a TGF alpha/EGFR-mediated autocrine growth pathway in cultured prostatic carcinoma cells. Studies of cultured prostate cancer cells, but not normal epithelial cells, demonstrate constitutive activation of EGFR. Androgen-independent cancer cells exhibit more EGFR expression and phosphorylation than do androgen-responsive prostate cancer cells. Most studies indicate that EGFR do not play a functional role in androgen-stimulated growth of prostate cancer cells. Several studies have correlated EGFR expression with increased nuclear size and tumor dedifferentiation. Future studies should focus on determining both the prognostic significance of EGFR expression and whether manipulation of EGFR-mediated growth can be exploited for therapeutic benefit in human prostate cancer.

Animals↗
PubMed1995

Human gamma X satellite DNA: an X chromosome specific centromeric DNA sequence.

The cosmid clone, CX16-2D12, was previously localized to the centromeric region of the human X chromosome and shown to lack human X-specific alpha satellite DNA. A 1.2 kb EcoRI fragment was subcloned from the CX16-2D12 cosmid and was named 2D12/E2. DNA sequencing revealed that this 1,205 bp fragment consisted of approximately five tandemly repeated DNA monomers of 220 bp. DNA sequence homology between the monomers of 2D12/E2 ranged from 72.8% to 78.6%. Interestingly, DNA sequence analysis of the 2D12/E2 clone displayed a change in monomer unit orientation between nucleotide positions 585-586 from a "tail-to-head" arrangement to a "head-to-tail" configuration. This may reflect the existence of at least one inversion within this repetitive DNA array in the centromeric region of the human X chromosome. The DNA consensus sequence derived from a compilation of these 220 bp monomers had approximately 62% DNA sequence similarity to the previously determined gamma 8 satellite DNA consensus sequence. Comparison of the 2D12/E2 and gamma 8 consensus sequences revealed a 20 bp DNA sequence that was well conserved in both DNA consensus sequences. Slot-blot analysis revealed that this repetitive DNA sequence comprises approximately 0.015% of the human genome, similar to that found with gamma 8 satellite DNA. These observations suggest that this satellite DNA clone is derived from a subfamily of gamma satellite DNA and is thus designated gamma X satellite DNA. When genomic DNA from six unrelated males and two unrelated females was cut with SstI or HpaI and separated by pulsed-field gel electrophoresis, no restriction fragment length polymorphisms were observed for either gamma X (2D12/E2) or gamma 8 (50E4) probes. Fluorescence in situ hybridization localized the 2D12/E2 clone to the lateral sides of the primary constriction specifically on the human X chromosome.

Base Sequence↗
PubMed1995

Growth suppression of human colorectal carcinoma in nude mice by monoclonal antibody C27-abrin A chain conjugate.

PURPOSE: The aim of this study was to assess an immunotoxin, monoclonal antibody C27-abrin A chain conjugate (MAAAC), that might be effective in the treatment of colorectal carcinoma. METHODS: The immunotoxin was prepared by a specific monoclonal antibody against carcinoembryonic antigen (CEA), monoclonal antibody C27, linked to N-succinimidyl-3-(2-pyridyldithio)propionate and then coupled covalently to the toxic abrin-A chain to synthesize MAAC. The therapeutic role of this immunotoxin in suppressing the in vitro and in vivo growth of CEA-secreting human colorectal cancer cells (LS174T) was assayed by methods of protein biosynthesis inhibition, cell colony proliferation, and treatment of tumor cells before and after inoculation in nude mice. RESULTS: We found that MAAC effectively suppressed the growth of LS174T in culture medium and completely eradicated cells in inoculated nude mice. In contrast, irrelevant immunotoxin antiferritin-abrin A chain conjugate and isotype-matched monoclonal immunoglobin (MOPC21IgG1)-abrin A chain conjugate did not cause such effects. The in vitro toxicity was highly specific because the conjugate (MAAC) inhibited de novo protein biosynthesis, impeded growth, and caused death of cells possessing surface CEA determinants. The 50 percent inhibition dose values of the conjugate for colonogenic survival and for protein biosynthesis in LS174T cells were 0.09 microgram/ml and 0.06 microgram/ml, respectively. Colon survival was inhibited 96.3 percent after prolonged MAAC treatment. MAAC showed selective cytotoxicity; the inhibitory effect of MAAC to the CEA-secreting LS174T cells over the CEA-nonsecreting human embryonic kidney cells was 16-fold. CONCLUSION: These results indicate that MAAC may be of benefit in therapy during or soon after resection of colorectal carcinoma or in patients who have micrometastasis.

Abrin↗
PubMed1995

Comparing the incommensurable: where science and politics collide.

Arguments about the possibility that cognitive variables may play a causal role in human behavior are unlikely to be resolved in favor of one side or the other, because they set against each other two incommensurable views of human agency. Contemporary cognitive models of psychology are based on an implicitly dualist view of human behavior, assuming the existence of a nonmaterial mental realm which has the capacity to act on the material world. Critics, by comparison, frequently argue from an epiphenomenalist position. While there may be sound scientific reasons for rejecting self-efficacy theory, and particularly for rejecting the utility of the concept that behavior is caused by efficacy expectations, this paper argues that epistemic criteria are frequently less important than a sense that a theory is compatible with a particular world view. I argue that cognitive theories are accepted by the psychological mainstream because their dualist basis accords with deeply held cultureal beliefs about the relationship between the person and the world. However, the social and political consequences of such models are rarely articulated, and there is a need for psychologists to develop a more explicit understanding of the relationship between psychological theories and their broader implications.

Cognition↗